Method of securing durable adhesions of liquid coatings to zinc surfaces



Patented Sept. 11,-1934 UNITED I STATES METHOD OF SECURING D URABLE AD- HESIONS F LIQUID COATINGS TO ZINC SURFACES Milford n. Corbin, Chicago, m., assignor to Ault & Wiborg Corporation, a corporationof Ohio No Drawing.

Application January 16, 1931, Serial No. 509,275

2 claims. (01. 91-68) This invention relates to a method of applying paints to zinc or zinc surfaced materials so that the paints will adhere to such surfaces. Metals of the zinc type. appear to be somewhat 5 peculiar among metals in that the paints or lacquers which are applied to surfaces of such metals become very short or brittle and crack or peel from the metal. If an oil-base material is used, zinc seems to accelerate the polymerization so that the paint does not long adhere, or if a pyroxylin-base material is used, the presence of the zinc seems to break it down. These dimculties have tended to limit the fields of usage of zinc and zinc coated materials.

The object of the invention is to provide a method of causing paints, enamels or lacquers, whether of an oil-base type or pyroxylin-base type, to adhere to zinc or zinc coated materials as the materials would do to ordinary metals.

The invention is predicated upon the discovery that this harmful .aifectation of the. paint or enamel or lacquer by the zinc is strictly interface phenomena and that either a thin coverage of the zinc surface with another metal or the dis- 5 placement of the zinc at the surface by other metals, provides a surface to which the paints or lacquers or enamels will adhere without deterioration.

For instance, the liquid coatings can be made to adhere to the zinc by electroplating a thin layer over the zinc of some other metal such as copper or nickel. The preferred method of this invention, however, is to displace zinc molecules at the surface and substitute for them other molecules which provide a surface to which the paints or the like will adhere without deterioration. This is accomplished by dipping the zinc in or contacting the zinc with a solution including salts of metals which interchange with the zinc due to the difference in electric potential be-' will readily adhere to it and will not deteriorateany more rapidly than on ordinary materials.

A still better surface is obtained by adding sodium thiocyanate to the solution as this results in the deposit on the zinc surface of both the nickel and nickel sulphide. A small amount of zinc chloride in the solution aids this deposition when the solution is new, though additional amounts ,need not be added during the continued use of the solution due to the fact that additional quantities are formed in the use'of the solution.

A typical formula is as follows:

6 oz. NHiCL,

4 oz. NiCla, 2 oz. NaCNS,

/2 oz. ZnClz,

1 gallon H2O.

A sulphate solution of salts including nickel salts, likewise provides a modification of the zinc surface of the same nature. A sulphate type bath should include nickel sulphate, a small quantity of zinc sulphate, sodium thiocyanate, and sodium acetate. A typical formula for sulphate baths is as follows:

-12 oz. NiSO4, 3 oz. NaCNS,

1 oz. NaCzHaOz, 4 oz. ZnSOs. 1 gal. H20.

In practice, the zinc is usually dipped in the treating solution for one-half minute at a temfirature of 100 F., after which it is washed and While this disclosure has been made chiefly in relation to zinc and oil-base or pyroxylin coating materials, it is adaptable for use in all cases where a specific coating material will not adhere to a specific metal as it will be readily understood by the skilled in the art that by selecting a solution of a salt of a metal having a potential different from that of the metal to be treated,

(in the nature of the potential difference between zincand the nickel salt solution), the replacement of surface molecules can be accomplished to inhibit the specific catalytic action whereby the surface molecules of zinc are retion containing, in one gallon of water, 6 oi. am-

monium chloride, 4 oz. nickel chloride, 2 oz.

sodium thiocyanate and oz. zinc chloride, whereby the surface molecules of zinc are replaced with surface molecules of nickel and nickel sulfide which will prevent the lacquer from being deteriorated by the zinc surface.

MILFORD H. CORBIN. 

